The invention concerns a reinforcing element for load-bearing or load-transferring structural components, the reinforcing element comprising a flat strip lamella secured to the surface of a structural component using an adhesive, the flat strip lamella comprising a plurality of reinforcing fibers embedded in a binder matrix and oriented parallel to each other and in the lamella longitudinal direction. The invention further concerns a process for securing this type of reinforcing element to a structural surface.
The reinforcing fibers, which are preferably comprised of carbon fiber, impart to the flat strip lamella a greater elastic extensibility.
Beginning therewith, it is the task of the present invention to develop a reinforcing element of the above-described type as well as a process for the securing thereof to a structural surface, such that an imprinted tensile stress can be reliably maintained during and after the hardening of the adhesive.
The inventive solution is based on the concept, that the flat strip lamella, on the basis of their large elastic extensibility of the reinforcing fibers, are particularly suitable for pre-tensioning and thus for improvement of the structural support relationship to the reinforced structural component. For this, the flat strip lamellas must be connected at their ends to anchor plates, which make possible the introduction of the pre-tensioning into the structural component, or a tensioning beam provided especially for this, during and after the hardening of the adhesive. In order to accomplish this, it is proposed in accordance with the invention, that each free end of the flat strip lamella respectively engages an anchor plate which via securing means is anchored on the structural unit or on a tensioning beam and thereby is secured against tensile and shear forces acting in the longitudinal direction on the lamella. Advantageously, the anchor plates are materially or chemically connected to the lamella ends, and preferably they are adhered to these. A further improvement of the connection between the anchor plates and the lamella ends can be achieved by force fittingly and/or formed fittingly connecting the anchor plates with the lamella ends, preferably by clamping and/or enclosing between two anchor parts. For production of a form-fitting connection, the lamella ends can respectively be provided with a widening and/or thickening, and the anchor plates with a recess for form-fitting reception of the widening and/or thickening.
In order to make possible a thin layer adhesive application, it is proposed in accordance with a preferred embodiment of the invention that the anchor plates are comprised of an at least a thin-walled floor part and a, in comparison to the floor part, thick-walled cover plate, externally flat and extending over the breadth of the lamella. Preferably, the cover plate is provided with the recess for reception of the widening or thickening of the flat strip lamella. For this purpose the anchor plates can be formed of two parts, wherein the two anchor parts are either adhered together or held together by screws.
A preferred embodiment of the invention envisions that the broadening and/or thickening of the lamella is formed by a divergent splitting of the reinforcing fibers and at the lamella free end, and in certain cases by a widening of the binder matrix in this area. The broadening and/or thickening can, however, also be formed by an application of material, preferably a synthetic resin, on the lamella ends.
In accordance with a further preferred embodiment of the invention it is envisioned that the anchor plates, at least in the area of the entry of the flat strip lamella, are elastic. Thereby, it is made possible that the tensile forces occurring in the transition area are maintained at a reliable level, in that the tensions within the end sections are gradually reduced. In order to achieve this, it is of advantage, when the stiffness at the end sections of the anchor plates at the entry points of the flat strip lamella are gradually reduced. This can be achieved for example in that the wall thickness and/or breadth of the cover part and/or floor part of the anchor plate becomes reduced in the end section towards the entry point of the flat strip lamella. The wall thickness of the floor part of the anchor plate at the entry side corresponds with the layer thickness of the adhesive layer provided on the construction component to be secured.
In accordance with a further advantageous embodiment of the invention it is envisioned that the anchor plates include an anchoring section adjacent the end sections, which is provided with a transverse bore for passage-through of the anchoring screws situated along the sides beyond of the there secured lamella end. During tightening of the securing screws, the lamella end is clamped between the floor part and the cover part of the anchor plate, so that besides the adhesive connection a force-fitting connection results. For improvement of the adhesive connection, it is of advantage when the lamella ends are adhered on both sides, with the cover part and with the floor part of the anchor plate.
A further variant of the invention envisions that the anchor plates include an at least partially flexible tube, preferably with right-angled internal cross-section, and two wedge elements pressed into the tube, and that the respective lamella ends are tensioned between the wedge surfaces of the wedge elements facing each other, and are adhered thereto. In addition, the wedge parts can also be adhered into the tube. A supplemental form-fitting is achieved thereby, that the each other facing wedge surfaces in the lamella longitudinal direction complementary to each other are curved. Therein, it is advantageous, when one of the two wedge elements extends only over a part of the tube length and that the other wedge element on its wedge surface exhibits a preferentially tangential engaging wedge surface which holds the flat strip lamella against the structural side of the tube wall and with this and the flat strip lamella is adhered and/or tensioned. In order to achieve an optimal flexibility of the anchor plates, the tube can be formed as a wrapped tube of glass fiber reinforced plastic. The tube and the wedge elements can be provided with transverse bore holes situated sideways outside of the lamella end for the passage-through of the securing and tensioning screws. In order to increase the flexibility of the anchor plates at the entry side tube end, it is of advantage, when the tube with wedge elements inserted exhibits a reducing wall thickness or breadth at the end section towards the entry side of the tube.
According to a further preferred embodiment of the invention, the flat strip lamellas can be acted upon with an electric current. For this, it is advantageous to construct the anchor plates to be electrically conductive such that they form a contact point for the connection of the carbon fibers to a source of electricity. In this manner, it is possible to accelerate the hardening of the adhesive by resistance heating of the flat strip lamella, and to also increase the thermal stability.
The binder matrix of the flat strip lamella is preferably comprised of a duroplast, preferably an epoxy resin. In principle, the binder matrix can also be a thermoplast, preferably selected from the group consisting of polyolefins, vinyl polymers, polyamide, polyester, polyacetate, polycarbonate, and thermoplastic polyurethane. The reinforcing fibers can, as already described, be carbon fibers. In principle, the reinforcing fibers could also be aramide fibers, glass fibers, or polypropylene fibers.
For maintaining a pre-tension in the flat strip lamella, the lamella ends are first force-, form- and/or materially-(chemically) engaged with the anchor plate. In accordance with a first process possibility, it is proposed that besides this one of the anchor plates is secured to the structural component, for example is screwed in and/or adhered, while the other anchor plate before or after application of adhesive is brought into engagement with a tensioning mechanism associated with the structural component and activated upon by a shear force for achievement of an elastic pre-tension in the flat strip lamella in the lamella longitudinal direction, whereupon the flat strip lamella pre-tensioned in this way is maintained or pressed against the structural component surface until hardening of the adhesive. A second alternative solution envisions that the anchor plates are first fixed to a tension beam with production of an elastic pre-tension in the flat strip lamella, and that the tension beam is pressed or held against the structural component surface with the adhesive side of the flat strip lamella until the adhesive hardens. According to a preferred embodiment of the invention, an electrical current is conducted though at least through a part of the reinforcing fibers during the hardening of the adhesive for heating of the flat strip lamella and the adhesive layer.
For production of the form-fitting engagement between the lamella ends and the anchor plates, the carbon fibers can, at the free ends of the previously cut-to-size flat strip lamellas, be freed of adhesive material, preferably using steam, and split apart forming a broadening and/or thickening, and in this condition, be fixed with a viscous, hardenable binder. The carbon fibers freed of binder matrix are thereby preferably spread apart until divergence at the free lamella ends. The carbon fibers freed of binder matrix are for this purpose preferably introduced into an undercut recess in the anchor plate and there positionally fixed and anchored with a binder which is viscous, hardenable, and at the same time serves as adhesive. The anchor plates are, after achieving a predetermined pre-tension, secured to the structural component or tension beam, preferably by screwing or adhering.